The present invention relates to a magnetic recording medium with high recording density, and in particular, to a removable type magnetic recording medium to be used in auxiliary memory unit, image storage unit, etc. of a computer. Further, the invention relates to a floppy disk using a flexible support member with high recording density of 1 GB or more per square inch.
With extreme increase in the capacity of electronic data prepared in devices such as personal computer, there are now strong demands on the development of a removable type disk comprising high capacity magnetic recording medium for the purpose of storing large amount of electronic data and for backup operation.
Up to now, digital video tape has been primarily used as ultra-high density recording medium for business use. With rapid increase in the amount of information in recent years, there are now demands on technical development to seek higher capacity and higher speed for recording and reproduction. Instead of the video tape currently used as main stream in this field, attempts are now being made to use removable type disk with better recording and reproducing speed as a digital recording medium for business use.
On the other hand, in the high density magnetic recording medium of GB class currently in use, a disk made of aluminum, glass, etc., i.e. the so-called hard disk, is used. When shock is applied on the device, head crash may occur, and both medium and head may be subjected to serious damage. This problem of shock-resistant property is not yet overcome in the removable type hard disk, and this has hindered the use as recording means in portable devices such as digital disk camera.
When the support member is changed from hard disk to a flexible member of the same type as a floppy disk, it is advantageous in that the recording unit can be produced in lightweight design, and damage at head crash can be alleviated. In this respect, there are now strong demands on the development of high density removable type magnetic recording medium using a flexible support member with high shock-resistant property as substrate.
In a removable type magnetic recording medium, a magnetic layer comprising a ferromagnetic metal or alloy is formed on a substrate. In particular, in the high density magnetic recording medium, for a ferromagnetic layer formed on the magnetic recording medium, a magnetic layer is formed by vacuum film forming method.
However, in the removable type magnetic recording medium using a flexible support member, there have been problems in that cracking occurs during manufacturing process and the product cannot be used as a medium.
It is an object of the present invention to provide a floppy disk type magnetic recording medium with high quality in a removable type high density magnetic recording medium using a flexible support member as substrate, and to prevent cracking in the manufacturing process.
The above problems can be solved by a floppy disk, which comprises a primer layer, a magnetic layer, a protective layer, and a lubricating layer coated on at least one of the surfaces of a flexible nonmagnetic support member, whereby a seed layer is provided between the flexible support member and the primer layer.
Also, the present invention provides a floppy disk as described above, wherein there is provided a flattening layer, comprising a heat-resistant polymer on the flexible nonmagnetic support member.
Further, the present invention provides a floppy disk as described above, wherein the thickness of the flexible support member is within the range of 30-100 xcexcm.
Also, the present invention provides a floppy disk as described above, wherein a Coxe2x80x94Cr alloy with a Cr concentration within the range of 10-30 atom % is used for the magnetic layer.
Further, the present invention provides a floppy disk as described above, wherein a Cr alloy with a Cr concentration within the range of 77-100 atom % is used as the primer layer.
Also, the present invention provides a floppy disk, which comprises a flattening layer with a thickness of 0.1-5 xcexcm, a seed layer, a nonmagnetic primer layer containing a Cr alloy with a Cr concentration of 77-100 atom %, a magnetic layer containing a Coxe2x80x94Cr alloy with a Cr concentration of 10-30 atom %, a protective layer, and a lubricating layer, all of said layers being coated on at least one of the surfaces of a flexible support member with a thickness of 30-100 xcexcm, whereby the thickness of the seed layer is 5-100 nm, and the linear expansion coefficient (ESE) of the seed layer and the linear expansion coefficient (EUL) of the nonmagnetic primer layer satisfy the relation: |ESExe2x88x92EUL|/xe2x88x92EUL less than 0.3, and the tensile strength (SSE) of the seed layer and the tensile strength (SUL) of the nonmagnetic primer layer satisfy the relation: SSE/SUL greater than 1.